From 176505b897edea2dd0e7ad49349defdebae55ca1 Mon Sep 17 00:00:00 2001
From: Simon Gardling <titaniumtown@proton.me>
Date: Tue, 18 Feb 2025 20:13:19 -0500
Subject: [PATCH] MAJOR (25%+) perf increase with propegate iterator and copies

---
 src/board.rs | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/board.rs b/src/board.rs
index be64167..9e42443 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -166,7 +166,7 @@ impl Board {
     }
 
     /// Get a reference to a backing [`BitBoard`]
-    pub const fn board(&self, color: Piece) -> &BitBoard {
+    const fn board(&self, color: Piece) -> &BitBoard {
         match color {
             Piece::Black => &self.black_board,
             Piece::White => &self.white_board,
@@ -174,7 +174,7 @@ impl Board {
     }
 
     /// Get a mutable reference to a backing [`BitBoard`]
-    pub const fn board_mut(&mut self, color: Piece) -> &mut BitBoard {
+    const fn board_mut(&mut self, color: Piece) -> &mut BitBoard {
         match color {
             Piece::Black => &mut self.black_board,
             Piece::White => &mut self.white_board,
@@ -249,13 +249,19 @@ impl Board {
             return 0;
         };
 
-        let pos_s: Vec<(usize, usize)> = self.propegate_from_dry(i, j, starting_color).collect();
-        let pos_len = pos_s.len();
-        for (i, j) in pos_s {
+        // PERF! avoid clones and collections here using raw pointers
+        let iterator = unsafe {
+            // SAFETY! `propegate_from_dry` should not have overlapping chains
+            // if overlapping chains were to exist, `self.place_unchecked` could collide with `self.get`
+            (&*(self as *const Self)).propegate_from_dry(i, j, starting_color)
+        };
+        let mut count = 0;
+        for &(i, j) in iterator {
             self.place_unchecked(i, j, starting_color);
+            count += 1;
         }
 
-        pos_len
+        count
     }
 
     /// Propegate piece captures originating from (i, j)
@@ -266,7 +272,7 @@ impl Board {
         i: usize,
         j: usize,
         starting_color: Piece,
-    ) -> impl Iterator<Item = (usize, usize)> + use<'_> {
+    ) -> impl Iterator<Item = &(usize, usize)> + use<'_> {
         ADJ_LOOKUP[i][j]
             .iter()
             .filter_map(move |chain| {
@@ -281,7 +287,6 @@ impl Board {
                 end_idx.and_then(|idx| chain.get(..idx))
             })
             .flatten()
-            .cloned()
     }
 
     /// Count the number of a type of [`Piece`] on the board